Recycled asphalt waste is a known additive for the production of asphaltic paving compositions used in the construction of roads, highways, bridges, airport runways, parking lots, playgrounds, and other rolling surfaces that require a bituminous coating. An emphasis in using recycled asphalt shingles (RAS) in pavement construction has reduced the environmental liability of RAS and has further reduced the amount of virgin asphalt used in pavement construction. In the U.S., it is estimated that about 11 million tons of RAS are produced annually. The asphalt in RAS and also recycled asphalt pavement (RAP) is known to be much stiffer than virgin asphalt. This has led to increased stiffness of asphaltic paving compositions. The stiffer the paving composition, the more difficult it is to place and the more susceptible it is to cracking at lower temperatures.
Typical petroleum based, softening agents are known to enable the use of larger amounts of recycled asphalt waste, such as RAS and RAP in the formulation of a performance grade (PG) asphalt. The cost of the petroleum based softening agents can be expensive and their use continues to raise environmental concerns. As such, bio-oils and other organic materials are now being used as asphalt softening agents. Some of the various bio-oils and organic materials include vegetable oils and starches, as well as lignin and cellulose.
Storage stable asphalt pellets made from RAS have also advanced the pavement industry. For example, in the production of prilled pellets from RAS, the non-shingle debris, roofing felt, asbestos containing material, and fiberglass can be removed to form a quality material RAS pellet. RAS pellets that meet these quality material requirements are easier to handle and transport, and they can be stored in stockpiles at job sites and asphalt plants. In addition, the pellets are relatively the same size, enabling more accurate feed rates.
In asphalt production, final RAS product is subject to state law. Ostensibly, three commonly regulated requirements are gradation, extraneous waste materials, and moisture content. An example of a gradation requirement is a minimum percent; i.e., 95% or more of RAS pass a ⅜ inch sieve test. Regarding the extraneous waste materials requirement, this often includes a showing that the final RAS product is substantially free of extraneous waste materials and entirely free of whole, intact nails. The moisture content requirement usually requires moisture levels to not be considered excessive so as to negatively impact specified hot mix asphalt (HMA) moisture limits.
As more and more recycled asphalt waste is produced, there is a need to improve RAS containing asphalt mixes and improve RAS rheological properties to enable a larger amount of RAS to be used in a PG asphalt mix.